Bentley B.R.2
 

Jane's, in engines' section mention a 250 HP at 1250 RPM as power output. Same source, in caption of a Snipe photo, mention 230 HP, while text on same page cites 200 HP.

Anybody knows real brake horsepower (and related RPM) developed by this engine?

Thanks,
GB

S! Sir,

It would seem that, according to Alec S. C. Lumsden, MRAeS, British Piston Aero-Engines (quoted as reference by: Bentley B.R.2 - Wikipedie, otevřená encyklopedie ), the powers for Bentley B.R.2 were (translated from the wikipedia):

flight: 230 hp (171,5 kW) at 1300 rot/min
max: 234 hp (174,5 kW) at 1350 rot/min

The 'National Museums Scotland' page also mentions the 230 hp figure:

Search Results

As these links are online, perhaps you already visited them.

Regards,
Gabi

Hi Greybeard,

The Bentley B.R.2 was rated 200 hp at 1250 rpm (British Air Board):

http://img.photobucket.com/albums/v2...entley_BR2.jpg

As Laser noted, the higher power ratings were for maximum output.

Curiously, Glenn D. Angle in Airplane Engine Encyclopedia mentions between 230-250 hp.

Airplane Engine Encyclopedia; an ... - Google Book Search

Andrew Nahum, 'The rotary aero engine' (HMSO,1987) states that the BR2 was rated at a nominal 200 hp, normal max. power was 230 hp at 1300 rpm, but it had a "maximum output of over 230 hp". So, I would guess the answer is:

Nominally 200 hp at 1250
Normal maximum 230 hp at 1300
Full maximum (a few minutes only) 234 hp at 1350

Bletchley

The BR1 was nominally 150 hp at 1250 rpm (Air Board figure, but Nahum has 158 hp at 1250 although I think this may have been the high compression version of this engine), but it could reach 1300 rpm 'for a few minutes only' (Air Board), although I have no figure for the hp at this engine speed. In his memoirs W.O. Bentley stated that a further 11 hp was gained by drilling a small hole in one of the induction pipes of the BR1, and "We sent the word round and fitters on every B.R. squadron were soon busy with little 2-mm drills" (Bentley, W.O. The autobiography of W O Bentley, Hutchinson, 1958).

The Clerget 9BF that Bentley was associated with also produced more power than it's nominal 130 hp. Gwynnes rated it at 150 hp, although it appears to have produced 'only' 140 hp at normal max. speed, 1250 rpm, 160 hp for 'a few minutes only' (compared to 134 or 135 hp at normal max. speed, 150 hp for a few minutes only, for the original French built Clerget 9B). Gwynnes Ltd, Clerget patent aero engines, 9b & 9BF, 1917 (reprinted by Camden Miniatures, 2001).

Graham Mottram, Director of the Fleet Air Arm Museum, has written a useful pamphlet 'W.O. Bentley's aero-engines' (W.O. Bentley Memorial Foundation, publication no.3, 2003), that has a lot of very useful information on the BR1 and BR2 and Clerget 9BF.

Perplexing Data
 

GB, I hope your not as perplexed as I'am from the submitted data!

Bentley B.R.2 - 140mm bore, 180mm stroke, 24.9l disp, 5.2:1 CR

BHP ------- RPM -------- Source
200 ------- rated ------- Aero 1939
200 ------- 1250 ------- The Rotary Aero Engine(TRAE),British Air Board1917
230 ------- 1300 ------- Aero 1939,The Airplane Engine 1922, TRAE
234 ------- 1350 ------- TRAE, and others
250 ------- 1250? ------- Jane's 1919

The Jane's listing clearly shows a display sign showing the advertised BR2-250hp model. However, it doesn't show at what RPM that was claimed! Jane's happens to report it at 1250rpm. But I believe we can discount that as incorrect.

Anyway, my main point would be the 200 - 230bhp jump in only 50 rpm.

That's a 15% increase in bhp for a 4% increase in revolutions. Sure wish I could do that!!! (or my wife wishes it)

As your already aware something doesn't look or fit right!:rolleyes:

How, do you see all this working out?

Happy Holidays,

KC

Thanks you all a lot for help!

Mainly, what surprises me is how no test bench record seems survived of this "grand" engine (that Snipe used up to 1927, if my memory serves).

Then, I tend to rely on lowest value (230 HP), since, looking all sources agreeing on B.R.1 power output of 150 HP, ratio made by related displacements of the two engines, gives 216 HP as calculated power and 224 HP if a 1300 RPM is supposed (in relationship to 1250 RPM of B.R.1).

Perhaps some further HP was provided by some increase in compression ratio?

GB

I think the 200 hp at 1250 rpm was entirely "notional" or nominal - just a paper figure (rather like Gwynnes' nominal 150 hp at 1250 rpm for the Clerget 9 and 9BF). The British Air Board data for the BR2 from 1917 is contained in the "experimental" data sheet, and is also probably not to be trusted (it is very probably just an indication of what was expected, based on the design figures and perhaps early prototypes). There were two versions of the BR1, a lower and a higher compression - both of which were used operationally - but so far as I am aware only one version of the BR2 at this time, although there is a hint in the National Archives catalogue that a higher compression BR2 with a benzol / petrol fuel was experimented with but soon abandoned in the early 1920s.

The difference in hp between normal maximum and full maximum rpm (a few minutes only) was often very small for rotaries, apparently due to windage, although as KC says you couldn't really expect much of an increase from 50 rpm at or near the top of the power curve, so an increase from 230 hp at 1300 rpm to 234 hp at 1350 sounds about right to me.

Bletchley

I agree. Thanks,
GB

Actually, rotary engine power curves were very steep compared to water-cooled engines of the era, and the contrast in performance is even greater in relationship to modern high-rpm engines.

From NACA Technical Memorandum No. 11, which was a translation from the wartime Nachrichten fur Luftfahrer, comes the following data on the Goebel Rotary engine series. As can be seen from the included chart, the Goe III engine rated at 200 hp at 1150 rpm, gains 30 hp when running at 1200 rpm (this is in a 50 rpm increase) . It remains plausable therefore, that the Bentley B.R.2 of similar horse power also had similar power increases (and this is what the historical data indicates):

http://img.photobucket.com/albums/v2...tary_Power.jpg

I checked the references to a high compression BR2 in the National Archives catalogue, and they are:

AVIA 6/4738 'Comparative tests on aviation spirit and F.12 spirit (20% benzol) on B.R.2 engine no.50002' 1919

AVIA 6/5162 'Performance tests of B.R.11 high compression engine in Snipe aeroplane' 1919

I havn't looked at these documents, but this later 'high compression' engine might well have developed 250 hp or so, explaining Jane's 1919 reference to a 250 hp BR2. But I have never come across any other reference to a 250 hp BR2 engine.

There are a number of manuals and performance test reports on the BR2 in the National Archives, Greybeard, but I guess no one has yet got around to publishing them.

Bletchley